Date: Sat, 20 Aug 2011 12:33:29 -0500 From: Alan Cox <alan.l.cox@gmail.com> To: "Alexander V. Chernikov" <melifaro@ipfw.ru> Cc: Kostik Belousov <kostikbel@gmail.com>, freebsd-stable@freebsd.org, perryh@pluto.rain.com, daniel@digsys.bg Subject: Re: 32GB limit per swap device? Message-ID: <CAJUyCcMc7m65c_XjHNFi0A4cHHySC1brLS7HdivstxeOi6uFQw@mail.gmail.com> In-Reply-To: <4E4CCA6C.8020408@ipfw.ru> References: <4E4143A6.6030307@digsys.bg> <935F8EC2-88E0-45A3-BE8B-7210BE223BC5@mac.com> <4e42a0c0.e2t/9MF98O3HFjb1%perryh@pluto.rain.com> <4E4CCA6C.8020408@ipfw.ru>
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On Thu, Aug 18, 2011 at 3:16 AM, Alexander V. Chernikov <melifaro@ipfw.ru>wrote: > On 10.08.2011 19:16, perryh@pluto.rain.com wrote: > >> Chuck Swiger<cswiger@mac.com> wrote: >> >> On Aug 9, 2011, at 7:26 AM, Daniel Kalchev wrote: >>> >>>> I am trying to set up 64GB partitions for swap for a system that >>>> has 64GB of RAM (with the idea to dump kernel core etc). But, on >>>> 8-stable as of today I get: >>>> >>>> WARNING: reducing size to maximum of 67108864 blocks per swap unit >>>> >>>> Is there workaround for this limitation? >>>> >>> > Another interesting question: > > swap pager operates in page blocks (PAGE_SIZE=4k on common arch). > > Block device size in passed to swaponsomething() in number of _disk_ blocks > (e.g. in DEV_BSIZE=512). After that, kernel b-lists (on top of which swap > pager is build) maximum objects check is enforced. > > The (possible) problem is that real object count we will operate on is not > the value passed to swaponsomething() since it is calculated in wrong units. > > we should check b-list limit on (X * DEV_BSIZE512 / PAGE_SIZE) value which > is rough (X / 8) so we should be able to address 32*8=256G. > > The code should look like this: > > Index: vm/swap_pager.c > ==============================**==============================**======= > --- vm/swap_pager.c (revision 223877) > +++ vm/swap_pager.c (working copy) > @@ -2129,6 +2129,15 @@ swaponsomething(struct vnode *vp, void *id, u_long > u_long mblocks; > > /* > + * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks. > + * First chop nblks off to page-align it, then convert. > + * > + * sw->sw_nblks is in page-sized chunks now too. > + */ > + nblks &= ~(ctodb(1) - 1); > + nblks = dbtoc(nblks); > + > + /* > > * If we go beyond this, we get overflows in the radix > * tree bitmap code. > */ > @@ -2138,14 +2147,6 @@ swaponsomething(struct vnode *vp, void *id, u_long > mblocks); > nblks = mblocks; > } > - /* > - * nblks is in DEV_BSIZE'd chunks, convert to PAGE_SIZE'd chunks. > - * First chop nblks off to page-align it, then convert. > - * > - * sw->sw_nblks is in page-sized chunks now too. > - */ > - nblks &= ~(ctodb(1) - 1); > - nblks = dbtoc(nblks); > > sp = malloc(sizeof *sp, M_VMPGDATA, M_WAITOK | M_ZERO); > sp->sw_vp = vp; > > > (move pages recalculation before b-list check) > > > Can someone comment on this? > > I believe that you are correct. Have you tried testing this change on a large swap device? Alan
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